Valve assemblies which are required in conduit systems through which high temperature and high pressure fluids flow, e.g. 1600.degree. F. and 105 psi, must not only have the requisite strength to withstand the high internal pressure but must be heat insulated so that the outer surfaces are relatively cool, e.g. 250.degree. F., for safety reasons. Additionally, the valve structure must be such as to maintain functional integrity in spite of differential thermal expansion and contraction of the valve assembly components.
Accordingly, it is an object of the present invention to provide a valve assembly which is capable of withstanding high temperature and high pressure fluids therein. Another object of this invention is to provide a valve assembly in which functional integrity of the valve assembly is maintained during differential thermal expansion and contraction of the valve assembly components. A further object of the present invention is to provide a valve assembly which has an outer surface temperature substantially less than the temperature of the fluid within the valve assembly.